Described below is a novel material for the photoactive layer in organic photodiodes, to the use of the material and to an organic photodiode.
Organic photodiodes are known, for example, from EP 06792696.4. Disclosed therein are organic-based photodiodes built on a commercial transistor matrix with silicon-based transistors, as are commercially available inexpensively, as a substrate with the aid of a passivation layer. The organic photodiodes themselves include at least one first electrode layer on the substrate, an organic active layer thereon, on which a second electrode layer has been applied, and finally an encapsulation.
The known organic active layers include what is called an organic bulk heterojunction, which connects a hole conductor to an electron injection material.
These known photodiodes, however, are suitable only for the UV/VIS spectral range, and so there is a need to provide photodiodes which absorb higher wavelengths.
There is currently no efficient absorber for organic photodiodes in the near infrared range from 750 nm to 1000 nm on the market. This spectral range is of interest for optical industrial sensors among other applications.
Recently, the use of squaraines in organic solar cells was disclosed by three publications, one by Fabio Silvestri, Michael D. Irwin, Luca Beverina, Antonio Facchetti, Giorgio A. Pagani, and Tobin J. Marks; J. Am. Chem. Soc., Article ASAP; available at pubs.acs.org on Dec. 16, 2008; with the title “Efficient Squaraine based Solution processable Bulk-Heterojunction Solar Cells”; another by Anthony Burke, Lukas Schmidt-Mende, Seigo Ho and Michael Grätzel; Chem. Commun., 2007, 234-236 with the title “A novel blue dye for near-IR “dye-sensitised” solar cell applications” and finally a publication by Siyi Wang, Elizabeth I. Mayo, M. Dolores Perez, Laurent Griffe, Guodan Wei, Peter I. Djurovich, Stephen R. Forrest, Mark E. Thompson, APPLIED PHYSICS LETTERS 94, 233304, 2009 with the title “High efficiency organic photovoltaic cells based on a vapor deposited squaraine donor”.
However, the use of the squaraines disclosed therein did not lead to the desired effect in organic photodiodes because either the quantum efficiencies in the wavelength spectrum above 700 nm of only an inadequate 20% showed that the dark currents are too high, or the wavelength ranges above 700 nm in question are not covered at all